Insulation and air sealing

Posted on February 27, 2017

If I’m starting to sound like a broken record, it’s because air movement is a big deal in our little house. We seal gaps because it makes for less moisture coming in from the outside and fewer drafts, AKA a warmer, drier house with less chance of mold. So we’ve spent a fair amount of time doing this to the inside as well as the outside.

We air sealed the inside of the house by spreading silicone sealant into gaps and cracks — most notably in the large spaces around the windows and doors. If the gap was wider than 1/2″, we filled it with backer rod first, and then spread sealant over it. Side note: if you ask for backer rod at Home Depot, there’s an 80 percent chance that whomever you talk to will have no idea what you’re talking about. This is a true fact.

Backer rod is essentially rope made from closed cell foam. It’s located in the plumbing section. Why? Beats me. I don’t know what plumbers use it for. Directions for non-plumbing use: Stuff it into the gap, making sure it can’t move easily. You want it to compress a little, no more than 20 percent. Push it in so that the gap you now have to fill with silicone is half the depth of the total crack width, i.e. if you have a 3/4″ wide gap, push the backer rod in so that the depth of your silicone will be 3/8″. Ta da! You’re done.

Spray foam is another method of sealing around windows and doors that most people seem to prefer. It’s widely available and you don’t have to be as precise as with backer rod and silicone. Unfortunately, it also off-gasses, and with one sensitive human and one baby living in the house, we decided that backer rod and silicone would be less likely to incur migraines/birth defects/baby popping out of mama like an alien.

Around the same time as we started interior air sealing, we began insulating the walls and roof. Again, spray foam seems to be most people’s methods of choice. The added bonus of spray foam insulation is that it firms up walls, so if you have a tiny house with a history of walls shifting, you might seriously consider spray foaming your wall cavities. In lieu of spray foam, though, we chose sheep’s wool insulation for the walls, and rigid foam board for the ceiling. Sheep’s wool because: a.) It’s sheep! It’s like wrapping our house in a sweater! and b.) It has the equivalent insulation value of fiberglass but it weighs less, it’s a renewable resource, it’s not hazardous to your health, and it manages water and bugs better than both fiberglass and cellulose. It’s more expensive, but not by much. We picked batts from Black Mountain Insulation, USA (non-affiliate link, just giving out their name for the curious).

These were easy to install. Seth and our friend Kenneth stapled them into the wall cavities. Where they didn’t fit, we tore them into pieces, including the plastic mesh screen used to give the batts some body. It was a quick installation, and there has been minimal slumping as the house has moved and shifted.

We’re not thrilled with using rigid foam board in our ceiling, those large sheets of styrofoam. They’re a pain in the butt to cut. They make a mess. They’re also not environmentally friendly, and rigid foam has a tendency to decrease in R-value over time. However, the insulation value is high even with the decrease, and we don’t have a very deep ceiling cavity. We needed something good there to help keep us warm, and once again spray foam was off the table. We compromised a bit here and used large sheets from Craigslist. They’re quite old, so any off-gassing or R-value drift is done and gone. We still have a few steps to go with the ceiling insulation though. Our plan is to purchase 1″ rigid foam board to go up underneath the cavities, thereby creating a ceiling with no cold spots due to thermal break from the wood rafters, and then install the tongue and groove ceiling over that. It will decrease the head space in our loft by about 2″, but I think it will be worth it. We’ve been using an electric heater so far this winter since our fireplace isn’t ready, and our electric bills are enormous! Thank goodness we don’t have a bigger house to heat.